1. Field of the Invention
The present invention relates to a jack-up platform of the type comprising a buoyant upper barge mounted so that it can be moved along the length of bearing legs, mechanical means for moving the legs relative to the barge, and a submerged storage tank intended to rest on the bottom.
It furthermore relates to a method of installing a submerged tank of a jack-up platform of the aforementioned type and to a method of raising such a tank.
2. Description of the Related Art
Such types of platform are used for operating oil fields. What happens is that before the extracted oil is transported, for example by boat, as far as land, the submerged tank is used for its temporary storage.
It is known practice for this purpose to provide a large-capacity storage tank on which the legs of the jack-up platform rest.
In known platforms, the tank is generally made with concrete walls. It forms a footing on which the rest of the platform rests.
When installing the platform, the storage tank is floated out separately to the site where the platform is to be installed. It is then submerged by weighting it down by filling it with water taken from the sea.
When the tank is resting on the bottom, the barge of the platform bearing the legs is floated out to a location over the tank. The legs are then lowered until their lower end rest on the upper surface of the tank. The barge is then jacked up above the water level.
Such a method of installing a platform is effective and well mastered. However, in the case of platforms which have to be moved around the oil field a number of times during their life, the storage tank cannot be reused.
This is because as the tank is independent, it is extremely tricky and risky to re-float it.
Thus, each time the platform is moved to a new site, it is necessary initially to install a new tank. This considerably increases the cost of re-siting the platform.
Furthermore, abandoning the submerged storage tank once the upper barge has been re-sited is harmful to the environment.